The extensive chemotherapy followed of hematopoietic stem cells reinjection (HSC) is one therapeutic option which the profit is well demonstrated in the treatment of children's solid tumors. It's one of the "standard" treatment of the following tumors: neuroblastoma, metastatic medulloblastoma, Ewing sarcoma, lymphoma in relapse; and because of the big chemosensibility of paediatric cancers, stays an important therapeutic option in the rhabdomyosarcoma in relapse or metastatic, nephroblastoma, etc. The stem cells can be taken in the blood by cytapheresis after mobilization with pharmacologic molecules. At present, the reference of the mobilization treatment is the G-CSF (Granulocyte colony-stimulating factor) in monotherapy during 4 to 6 days. His inconveniences are: lasted of the treatment (4 to 6 days), reproduction of the injections (1 to 2 subcutaneous injections daily), day variability of the peak of mobilization, this hematopoietic stimulation imposes to delay the chemotherapy. The plerixafor activates a massive and fast mobilization of the HSC ( hematopoietic stem cells)(between 6 and 11 hours after the injection). Currently, it's indicated in association with the G-CSF ( Granulocyte colony-stimulating factor)in case of mobilization failure. However, his big flexibility of use could be of a big interest in monotherapy at the child. To date, there is in our knowledge no data on the use of this molecule at the child.